1. Field of the Invention
The present invention relates to a powder sinter layered manufacturing apparatus. More specifically, the present invention relates to a powder sinter layered manufacturing apparatus for fabricating a three-dimensionally manufactured product by laminating multiple sintered thin layers on a manufacturing table.
2. Description of the Prior Art
In recent years, there is an increasing demand for layered manufacturing apparatuses which make it possible to manufacture components used in prototypes for functional tests, components used in a variety of products in small quantities, and the like.
As some examples of layered manufacturing apparatuses which meet such a demand, there are powder sinter layered manufacturing apparatuses and layered manufacturing apparatuses applying ultraviolet curing resin (hereinafter referred to as a “stereolithography apparatus”). Among them, the powder sinter layered manufacturing apparatus has a major advantage of compatibility with various types of materials including rigid materials, unlike the stereolithography apparatus. Accordingly, powder sinter layered manufacturing apparatuses are gaining market recognition and being introduced to various applications.
FIG. 1 is a perspective view of a powder sinter layered manufacturing apparatus currently available in the market. As shown in FIG. 1, this powder sinter layered manufacturing apparatus is constituted of a laser beam emitting section 101A, a manufacturing section 101B, and a control device 101C.
The laser beam emitting section 101A is provided with a laser beam light source 1 and a mirror 2 for controlling a direction of irradiation of the laser beam.
The manufacturing section 101B includes a manufacturing container 3 which is disposed in a central part and used for manufacturing by irradiation of the laser beam to fabricate three-dimensionally manufactured products, and powder material containers 4a and 4b which are disposed on both sides of the manufacturing container 3 and used for storing powder materials. Moreover, a part table 5 is disposed inside the manufacturing container 3, and is configured to move up and down along inner walls of the manufacturing container 3. Feed tables 6a and 6b are disposed inside the powder material containers 4a and 4b, and are configured to move up and down along inner walls of the powder material containers 4a and 4b.
The control device 101C is configured to supply a powder material 8 onto the part table 5 with a recoater 7 by lowering the part table 5 in an amount equivalent to one thin layer while raising the feed table 6b, to form a powder material thin layer 8a on the part table 5. Then, the control device 101C is configured to selectively heat and sinter the powder material thin layer 8a on the basis of slice data (a drawing pattern) for a three-dimensionally manufactured product by using the laser beam and the control mirror 2. Further, the control device 101C is configured to repeat the foregoing operations as appropriate so as to form the three-dimensionally manufactured product. The control device 101C, after forming the three-dimensionally manufactured product in this way, is configured to cool down by cooling means in the end.
In general, the above-described powder sinter layered manufacturing apparatus has a smaller manufacturable XY-plane area in the manufacturing container 3 in comparison with a stereolithography apparatus. For example, one of the most popular large-size stereolithography apparatuses can deal with the maximum manufacturing size of an XY-plane area of up to 600 mm×600 m. On the other hand, a typical powder sinter layered manufacturing apparatus can only deal with an XY-plane area up to 380 mm×330 mm.
Incidentally, there is a growing demand in recent years for integrally manufacturing a large-size product which has not been manufacturable with a conventional apparatus. For this background, large-size powder sinter layered manufacturing apparatuses having the maximum manufacturable XY-plane area of 550 mm×550 mm, which is almost equivalent to the maximum manufacturable size of the stereolithography apparatuses, are being introduced to the market.
On the other hand, however, components used in prototypes for functional tests or products of many varieties in small quantities are not always suitable for such large-size layered manufacturing apparatuses. Many of those components or the like may be manufactured sufficiently within the conventional small plane area. In these cases, the following two problems are unavoidable with an increase in the XY-plane manufacturable size of the powder sinter lamination apparatuses.
(1) Increase in Cooling Time
A powder sinter layered manufacturing apparatus is configured to laminate powder material thin layers sequentially inside a manufacturing container, then to selectively heat and sinter the thin layers in order to fabricate a three-dimensionally manufactured product. Accordingly, the sintered thin layers and the unsintered powder materials remaining around the sintered thin layers are left inside the manufacturing container. Unlike the stereolithography apparatus, the powder sinter layered manufacturing apparatus of this type is generally configured to set a surface temperature of a laminated object at a temperature lower than the melting point of a manufacturing material by around 10° C., and to manufacture a product while controlling the temperature on the entire XY plane of the manufacturing container to be even. These operations are conducted in order to prevent warpage of a manufactured product and to effectuate manufacturing even by making a laser output relatively smaller. In this case, after completion of manufacturing, if the manufactured product is rapidly cooled down or if the manufactured product is taken out in a state where the manufactured product is not completely cooled down, the temperature may become uneven between the inside and outside of the manufactured product. Such a condition may lead to distortion of the manufactured product caused by consequent thermal stress or may complicate maintenance of accuracy.
To avoid these problems, it is essential to cool the manufactured product naturally and slowly down to an appropriate temperature for allowing an operator to take out the product out of the powder materials after manufacturing is complete. As for a guideline of such natural cooling time, a cooling period of about 20 hours is required for manufacturing by use of a manufacturing container capable of manufacturing a model having the manufacturable XY plane of 380 mm×330 mm and a manufacturable depth in the Z direction of 400 mm, for example. Meanwhile, it can be said that, when the depth in the Z direction is not extremely shallow in comparison with the manufacturable plane area, the cooling time is extended in proportion to the plane area thereof. For example, the plane area of the XY plane of 380 mm×330 mm is equal to 125,400 mm2 while the plane area in the case of 600 mm×600 mm is equal to 360,000 mm2. Accordingly, the latter area is about 2.9 times as large as the former area and the cooling time is also extended in proportion to this ratio. In addition, when manufacturing a product by use of the manufacturing container capable of manufacturing a model having the larger manufacturable plane area as mentioned above and the depth in the Z direction of 400 mm, which is the same as that mentioned above, the cooling time should require about 58 hours.
As described above, the cooling time is increased and the time for actually taking out the manufactured product is therefore delayed in case of using the manufacturing container having the unnecessarily large manufacturable XY-plane area in spite of manufacturing only a small object. Such an increase in time leads to a decline in operating efficiency.
(2) Alteration of Materials
In the case of a stereolithography apparatus, photocuring resin is heated up to approximately 40° C. and controlled at a constant temperature in order to promote a curing reaction at a portion subjected to irradiation of an ultraviolet laser and to maintain a fablication liquid level. Here, it is safe to say that alteration of materials caused by such a temperature rise is very little.
In the case of the powder sinter layered manufacturing apparatus, the entire surface of the powder material inside the manufacturing container is set to a temperature lower than the melting point of that material by around 10° C. For example, in the case of nylon used as a principal material of the powder sinter layered manufacturing apparatus, the entire surface is set to a relatively high temperature around 180° C. As a consequence, the powder material once used for manufacturing is altered by heat and has to be discarded as the case may be. Therefore, when manufacturing a small manufactured product relative to the maximum manufacturable plane area with the powder sinter layered manufacturing apparatus, the powder material may be wasted more than necessary.
As described above, in the case of manufacturing a manufactured product having a small plane area, the powder sinter layered manufacturing apparatus provided with the unnecessarily large manufacturing container may incur an increase in the cooling time and waste of the originally reusable powder material due to alteration in the quality. On the other hand, installation of an additional small-size powder sinter layered manufacturing apparatus to accommodate fabrication of smaller components causes problems in terms of expenses for installation, operating efficiency of the apparatuses, spaces for installation, and so forth.